text: Due to differential uptake in plants as well as marine carbonates of C, it is possible to use these isotopic signatures in earth science. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. In aqueous geochemistry, by analyzing the δC value of carbonaceous material found in surface and ground waters, the source of the water can be identified. This is because atmospheric, carbonate, and plant derived δC values all differ. In biology, the ratio of carbon-13 and carbon-12 isotopes in plant tissues is different depending on the type of plant photosynthesis and this can be used, for example, to determine which types of plants were consumed by animals. Greater carbon-13 concentrations indicate stomatal limitations, which can provide information on plant behaviour during drought. Tree ring analysis of carbon isotopes can be used to retrospectively understand forest photosynthesis and how it is impacted by drought.
  In geology, the C/C ratio is used to identify the layer in sedimentary rock created at the time of the Permian extinction 252 Mya when the ratio changed abruptly by 1%. More information about usage of C/C ratio in science can be found in the article about isotopic signatures.
  Carbon-13 has a non-zero spin quantum number of ½, and hence allows the structure of carbon-containing substances to be investigated using carbon-13 nuclear magnetic resonance.
  The carbon-13 urea breath test is a safe and highly accurate diagnostic tool to detect the presence of Helicobacter pylori infection in the stomach. The urea breath test utilizing carbon-13 is preferred to carbon-14 for certain vulnerable populations due to its non-radioactive nature.